Mountable vehicle body parts are attached to a vehicle body so that the part defines the outer, visible skin of the vehicle after it is installed. Ideally, these mountable vehicle body parts should be relatively lightweight, match visually with adjoining painted parts in the vehicle and have high surface quality (i.e., have a “Class A” surface finish). The mountable vehicle body parts should also have good thermal properties and good sound insulation properties. Plastic composite parts have been particularly advantageous in incorporating these desired properties.
The properties of mountable vehicle body parts have made them particularly suitable for roof modules, including roof modules having a sliding roof unit as well as lamella roofs. Although the description below focuses on roof modules, the description is also applicable to other mountable vehicle body parts, such as vehicle doors and flaps (e.g., engine hoods, trunk lids).
Currently known roof modules are manufactured as a composite part having an outer portion made of a dyed plastic sheet. The outer portion of the sheet is visible when the roof module is installed to the vehicle body. The dye preferably penetrates the entire thickness of the sheet. A fiber-reinforced plastic backing, such as a backing made from polyurethane reinforced with glass fiber, is attached to an inner surface of the plastic sheet. The glass fibers may be injected into the polyurethane by a long fiber injection (LFI) method so that the fibers contact the inside surface of the plastic sheet. Ideally, the plastic sheet should be kept as thin as possible to minimize the weight of the vehicle part, but any fibers that are not arranged parallel to the outer surface can be seen through the plastic sheet if the sheet is too thin. Further, direct contact between the fibers and the inner surface of the plastic sheet may create small bumps on the outer surface of the plastic sheet, diffusing light incident on the plastic sheet and creating a dull appearance. Existing mountable vehicle body parts use a plastic sheet that is thick enough to prevent the fibers contacting the sheet from appearing on the outer surface, but the added thickness adds undesirable weight to the vehicle part.
There is a desire for a mountable vehicle body part which meets the high visual specifications with regard to its outer appearance while still minimizing the weight of the part.